U.S. patent application Ser. No. 09/334,116 filed Jun. 15, 1999, and three commonly assigned U.S. patent applications of even date are directed to similar subject matters, and the contents of these applications are incorporated herein by reference.
The present invention relates to a vehicle occupant restraint system adapted to be fitted to a vehicle seat to prevent a vehicle occupant from slipping forward under the seat belt in case of an impact situation such as a vehicle crash, and a power actuator for instantaneously driving a driven member for such a device and other high speed mechanisms.
It is known that the so-called submarine phenomenon may occur in an impact situation such as a vehicle crash by the vehicle occupant slipping forward under the seat belt, and the waist belt failing to restrain the pelvis of the vehicle occupant. This is prone to occur when the occupant sits in the front end of the seat or when the back rest is tilted rearward, and reduces the effectiveness of the seat belt in restraining the vehicle occupant or prevents the desired parts of the vehicle occupant to be restrained.
Therefore, it is conceivable to raise the front end of the seat by providing a projection in a front end of the seat frame, or by installing a panel in a front end of the seat frame. However, a desired effect in preventing submarining may not be achieved if the projection or the panel is too low, and the comfort of the vehicle occupant may be impaired if it is too low.
It has been previously proposed to raise the front end of the seat only in case of an impact. Such proposals include those using an air bag (Japanese patent laid-open (kokai) publications No. 5-229378, No. 7-81466, and No. 3-322745), those which mechanically raise the front end of the seat (Japanese UM laid-open (kokai) publications No. 2-149328, No. 3-121947, and No. 4-93222), and those using a pyrotechnic actuator to mechanically raise the front end of the seat (Japanese UM laid-open (kokai) publication No. 3-61440).
A conventional power actuator 50 using high pressure gas is illustrated in FIG. 15. A cylinder 51 fixedly attached to a base member of the seat is provided with an inner bore 51a having a reduced diameter portion 51b in an intermediate part thereof, and receives a piston 52 in one end portion thereof. A free end 52a of the piston 52, which is integrally attached to the main body portion, for instance via a threaded engagement means, projects from an open end of the cylinder 51, and engages a front end of a seat via a link member or the like. The base end 52b of the piston 52 is provided with a somewhat enlarged diameter, and engages the inner circumferential surface of the cylinder inner bore 51a via an O-ring 53. The open one end of the cylinder 51 is fixedly closed by a cap 54 having a central opening 54a. The opening 54a slidably receives an intermediate part of the piston 52 so as to serve as a slide bearing for the movement of the piston 52.
The other end portion of the inner bore 51a of the cylinder 51 receives a propellant 55. The rear open end of the cylinder 51 is crimped on the rear end of the propellant via a retaining plate 57, serving also as a seal, and is thereby closed so as to keep the propellant 55 in place.
The above described structure is typically installed in a vehicle with the piston 52 pushed all the way into the bottom of the inner bore 51a of the cylinder 51. However, if the gap between the base end 52b of the piston 52 and the shoulder of the reduced diameter portion 51b is too small, some difficulty may be encountered in stalling the assembly to the vehicle due to possible dimensional errors in the various component parts of the pretensioner device (such as those found in the joints of the link members, the base member of the seat, and the cylinder retainer) and positional errors of the link members. If there is any play in the joint between the free end 52a of the piston 52 and the associated link member, and the joint between the link member and the buckle, impacts resulting from the cumulative effect of such plays may cause local plastic deformations, and energy loss of the high pressure gas.
Also, to prevent the vehicle occupant from being thrown forward in case of a vehicle crash or the like, it has been proposed to fit an automotive seat with a pretensioner device which is adapted to increase the restraint by the seat belt to restrain the forward movement of the vehicle occupant by rapidly pulling a buckle attached to a seat belt in the direction to increase the tension of the seat belt (U.S. Pat. No. 4,705,296).
Japanese patent laid open (kokai) publication No. 10-181527 discloses such a pretensioner device which is provided with a power actuator using a chemically produced high pressure gas for pulling a buckle. Such prior art devices involves some problems due to such plays. It is conceivable to install mechanisms to remove such plays in each device, but such mechanisms tend to increase the size of the device.
In view of such problems of the prior art, a primary object of the present invention is to provide a power actuator suitable for use in vehicle occupant restraint systems.
A second object of the present invention is to provide such a power actuator which is compact and capable of rapid actuation.
A third object of the present invention is to provide such a power actuator which is reliable in operation.
A fourth object of the present invention is to provide such a power actuator which is easy to install.
A fifth object of the present invention is to provide such a power actuator which can minimize an energy loss of its power source.
A sixth object of the present invention is to provide a vehicle occupant restraint system which is reliable in operation and easy to install.
According to the present invention, such objects can be accomplished by providing a vehicle occupant restraint system, comprising: a vehicle occupant restraint member moveable between a rest position and a deployed position; a power actuator supported by the seat frame for selectively driving the restraint member toward the deployed position; and a locking mechanism for retaining the restraint member substantially at the deployed position once the restraint member is deployed; the power actuator including a cylinder attached to the seat frame, a piston received in the cylinder, a propellant received in the cylinder to selectively applying a pressure to the piston, a piston rod extending from the piston and having a free end connected to the restraint member, and a spring member received in the cylinder to urge the piston out of the cylinder. The vehicle occupant restraint member typically consists of a slip preventing member, a seat belt buckle or an ELR device.
The spring member received in the cylinder effectively removes any play that may exist in the path of power transmission from the piston to the slip preventing member, and ensures a reliable operation of the system.
The present invention also provides a power actuator for rapidly actuating a driven member, comprising: a cylinder attached to the seat frame; a piston received in the cylinder; a propellant received in the cylinder to selectively applying a pressure to the piston, a piston rod extending from the piston and having a free end connected to the slip preventing member; and a spring member received in the cylinder to urge the piston out of the cylinder; a front end of the propellant is received in a central hole of the spring member.
Because the front end of the propellant is received in the central hole of the spring member, the volume of the chamber for the initial expansion of the combustion gas of the propellant is minimized, and the energy of the propellant can be efficiently utilized. Also, because the waste of the space between the piston and the propellant is minimized, it also contributes to the compact design of the power actuator. In particular, owing to the axial overlap between the spring member and the propellant, the axial length of the power actuator can be minimized. Typically, the driven member consists of a member for restraining a vehicle occupant in a vehicle crash situation, and the spring member consists of a compression coil spring.
According to a preferred embodiment, the front end of the propellant is received in the central hole of the spring member in such a manner that a gap is defined between the front end of the propellant and an opposing end of the piston in a fully compressed state of the spring member. Preferably, the propellant comprises a small diameter portion facing the piston, and a large diameter portion remote from the piston, a shoulder defined between the portions serving as a seat for the spring member. Therefore, even when an external force is applied to the piston rod or the piston, the propellant is protected from damage and deformation. The use of the shoulder of the propellant as a spring seat eliminates the need for a separate spring seat, and reduces the number of components parts.
When an inner bore of the cylinder includes a shoulder opposing the shoulder of the propellant, and a resilient annular seal member is interposed between the shoulders of the cylinder inner bore and the propellant, the positional error of the propellant can be favorably accommodated, and the precision required in the arrangement for closing the rear end of the cylinder is relaxed. In such a case, to simplify the manufacturing process of the power actuator, the other end of the cylinder adjacent to the propellant may be closed by crimping material of the piston over the propellant via a retaining plate.
For the convenience of handling of the power actuator, the piston rod may simply abut an opposing end of the piston so as to be readily separated therefrom, and an end of the inner bore remote from the propellant is larger than the piston rod but smaller than the piston in diameter. For instance, the piston rod may simply abut an opposing end of the piston via a spherical joint or a conical surface joint. Therefore, the alignment between the piston and the piston rod is automatically achieved, and the piston is protected from undesirable loads due to tilting of the piston. Also, the piston rod can be separated from the power actuator for shipment or other handling before the assembly work, and even in case of inadvertent ignition of the propellant, the piston simply moves inside the cylinder, and no harm or damage is done to other parts.
Normally, a vehicle occupant restraint member is required to maintain its deployed position once it is deployed. In view of this recognition, the power actuation may be provided with a one-way lock mechanism for preventing reversal motion once the piston rod is actuated.
Once the piston rod is assembled to the power actuator, it is preferable to provide a means for preventing inadvertent removal of the piston rod. To this end, a piston rod retaining member may be provided at an end of the cylinder remote from the propellant for resisting inadvertent movement of the piston rod during handling but permitting movement of the piston rod when the piston is actuated by the propellant.